428 Memoir Sears Foundation for Marine Research 



Range. Off west coast of North, Central and South America, Gulf of California to 

 Chile in the Pacific; equatorial Brazil in the Atlantic. 



Species. Six representatives of the genus from the Pacific Coast of America have 

 been given separate specific names. But it is still to be determined whether all of these 

 actually represent distinct species. "^ Two species have been described from the western 

 Atlantic and Caribbean. One of these, U. microphthalnium Delsman 1941, appears to 

 differ from all Pacific forms in its relatively much longer snout (p. 428). The other, 

 U.venezuelae Schultz 1949, resembles U. asterias (Jordan and Gilbert) 1883 of the 

 Pacific coasts of Mexico and Panama in general but differs from it in the less regular 

 arrangement and smaller size of the spines along the mid-dorsal line of the disc, and in 

 a relatively smaller eye (p. 432). 



Key to Western Atlantic Species 



I a. Snout in front of eyes about 1/3 ^s long as breadth of disc. Upper surface of disc 

 naked. tnicrophthalmum Delsman 1941, p. 428. 



I b. Snout in front of eyes only about V4 ^s long as breadth of disc. Upper surface 

 mostly prickly on disc and with a median row of slightly larger spines on disc and 

 on anterior part of tail. venezuelae Schultz 1949, p. 430. 



Urotrygon microphthalmum Delsman 1941 



Figure loi 



Study Material. None. 



Distinctive Characters. The only western Atlantic Rays with which Urotrygon 

 microphthalmum might be confused are Urotrygon venezuelae and Urolophus jamaicensis. 

 A longer snout and naked disc (see Key, p. 428) set it apart from U. venezuelae. It dif- 

 fers from Urolophus jamaicensis in the facts that : the contour of its disc is definitely 

 angular in front, with pointed snout and nearly straight anterior margins; its snout in 

 front of eyes is about twice as long as the distance between the eyes (only about as long 

 as the distance between the eyes in Urolophus jamaicensis^ ; its pectorals are angular in 

 outline; its caudal fin is narrower relatively; and its tail, from center of cloaca to tip, is 

 considerably longer than the distance from center of cloaca to tip of snout (shorter than 

 distance to snout in Urolophus jamaicensis^. 



Description.'^^''' Disc about as broad as long or a little longer, its anterior contour 

 angular; anterior margins nearly straight; posterior margins rather strongly convex; 

 outer and posterior corners well rounded; tip of snout pointed, projecting a little; 

 anterior angle in front of spiracles about 100°. Tail strongly depressed dorsoventrally 



seems probable. It was a nomen nudum, therefore, and it so continued until it was revived (with description) by 



Garman in 1913. 

 I n. For a recent survey of these Pacific species, see Beebe and Tee-Van (Zoologica N. Y., 26, 1941 : 264, and footnote), 



who remark "the species of eastern tropical Urotrygon are poorly known from a small number of specimens, and 



in those species where a larger number of specimens have been taken, there is considerable variation." 

 112. After Delsman (Mem. Mus. Hist. nat. Belg., [2] 3 Fasc. 21, 1941: 65, 66, fig. 8). 



